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JoelC707
Premium Member
join:2002-07-09
Lanett, AL

JoelC707

Premium Member

Convert 208:120 transformer to 240:120?

I have an APC SYTF2 step-down transformer. It was bought to use on a 208V UPS that we never obtained and so hasn't really been used. I currently don't have 208V available anymore and found out the hard way that this transformer doesn't output 120V on a 240V input (it gave me about 160V). Is it even remotely possible to modify this to work on a 240V input and give 120V out?

Other than getting a UPS that could take 240V in and give me 208V out (most will I believe, especially double conversion ones that only use the input for a charger), this is otherwise useless to me and while I don't exactly have a need for it, I'd like it to be useful in some way other than taking up space in a stack of servers in my shed.
iknow_t
join:2012-05-03

1 recommendation

iknow_t

Member

said by JoelC707:

I have an APC SYTF2 step-down transformer. It was bought to use on a 208V UPS that we never obtained and so hasn't really been used. I currently don't have 208V available anymore and found out the hard way that this transformer doesn't output 120V on a 240V input (it gave me about 160V). Is it even remotely possible to modify this to work on a 240V input and give 120V out?

Other than getting a UPS that could take 240V in and give me 208V out (most will I believe, especially double conversion ones that only use the input for a charger), this is otherwise useless to me and while I don't exactly have a need for it, I'd like it to be useful in some way other than taking up space in a stack of servers in my shed.

how could you lose 208V?? but since you lost that, the transformer is useless on a 240V system, and would have to be rewound(expensive) to work.. it will draw too much current, and overheat if used on a 240V system..

leibold
MVM
join:2002-07-09
Sunnyvale, CA
Netgear CG3000DCR
ZyXEL P-663HN-51

leibold to JoelC707

MVM

to JoelC707
Given that the maximum input voltage rating for the SYFT2 is 230V there isn't much that you can do that would make sense. In theory adding loops to the primary winding or removing loops from the secondary winding (probably multiple secondaries in this unit) could be done to adjust the transformer ratio. That is usually easier said then done.

I'm curious however about your 160V measurement. You shouldn't have gotten more then 140V output for a 240V input.
JoelC707
Premium Member
join:2002-07-09
Lanett, AL

JoelC707 to iknow_t

Premium Member

to iknow_t
said by iknow_t:

how could you lose 208V??

Because it's no longer at a commercial building with 3-phase power . It's now at my home with standard 120/240V service.
said by iknow_t:

the transformer is useless on a 240V system, and would have to be rewound(expensive) to work.. it will draw too much current, and overheat if used on a 240V system..

That's what I was afraid of. I didn't expect it to draw too much current but I only ever used it at it's present location once. I hung a couple of 120V UPSes off it and discovered they didn't like the input so I shut it off and haven't used it since.
JoelC707

JoelC707 to leibold

Premium Member

to leibold
said by leibold:

I'm curious however about your 160V measurement. You shouldn't have gotten more then 140V output for a 240V input.

It may have been 140V, this was a couple of years ago that I last tried it so I'm going from memory of what the multimeter said. I didn't realize the input range for it extended up to 230V (the APC spec site doesn't list that). The 120V UPS I had on it that didn't like the input was an SU1400RMXLNET which lists a normal mains input of 147V and a max configurable of 154V so I based my 160V recollection off of that. In theory, if it really did output 140V, the UPS shouldn't have complained.

aurgathor
join:2002-12-01
Lynnwood, WA

aurgathor to JoelC707

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to JoelC707
said by JoelC707:

Is it even remotely possible to modify this to work on a 240V input and give 120V out?

It depends on the number of windings and taps.

How many input and output connections do you see on the transformer?
JoelC707
Premium Member
join:2002-07-09
Lanett, AL

JoelC707

Premium Member

At the moment it's quite buried so I can't really answer that yet. I did have it open once after we got it (was curious as to what was in it) but I can't really recall if there was anything in there I could easily swap around or modify.

aurgathor
join:2002-12-01
Lynnwood, WA

aurgathor to iknow_t

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to iknow_t
said by iknow_t:

the transformer is useless on a 240V system, and would have to be rewound(expensive) to work.. it will draw too much current, and overheat if used on a 240V system..

I wouldn't say these without actually testing it, and verifying operation.

I'd say there is at least a 50% chance that it will work just fine on 240V without overheating, but with a 138.5V output.

And it may have multiple taps, so it may be possible to get it to work with very little extra effort.

Lastly, as for rewinding -- yes, a full rewinding most likely doesn't make any sense, but if the secondary is the outermost winding, it shouldn't be too difficult to remove 13% of the turns.
aurgathor

aurgathor to JoelC707

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to JoelC707
said by JoelC707:

At the moment it's quite buried so I can't really answer that yet. I did have it open once after we got it (was curious as to what was in it) but I can't really recall if there was anything in there I could easily swap around or modify.

Just open it up and post some pictures.

leibold
MVM
join:2002-07-09
Sunnyvale, CA
Netgear CG3000DCR
ZyXEL P-663HN-51

leibold to JoelC707

MVM

to JoelC707
If you do take it apart check just how many secondary windings it actually has. That number might range from 0 to 4 (0 in the case that it is actually wired as autotransformer, meaning that it doesn't have separate primary and secondary windings).

Since there are 4 output circuits (each 120V with 15A over current protection) you may be lucky and have 4 secondary windings. In that case it would be possible to take two of those 120V windings and wire them in series (in phase!) to use them as a 240V primary. You would need to cap the 208V winding (or install a 208V outlet if you so desire) and you would need to change the input circuit breaker to 15A (current rating of the secondary windings you are now using as primary). Total power of the transformer would be reduced to 3600VA and you lose 2 of the 4 output circuits but you would be able to use the device on 240V.
walta
join:2001-05-22
Saint Louis, MO

walta to JoelC707

Member

to JoelC707
I don’t understand why anyone would need this equipment.

The whole point of 208V power is 120 volts is available with no transformer necessary any one phase to neutral equals 120 volts.

With a l6-30p plug it is only connected to 2 phases and ground it would only be useful if the electrician had failed to pull a neutral wire.

I say send it to the recycler.

Walta

tschmidt
MVM
join:2000-11-12
Milford, NH
·Consolidated Com..
·Republic Wireless
·Hollis Hosting

tschmidt to JoelC707

MVM

to JoelC707
Neither the user manual or installation talks about changing taps but it can't hurt to open it up and look.

That being said I fail to see what value it has in a residential setting since you already have access to either 120 or 240v without the noise and losses associated with using a transformer.

/tom
JoelC707
Premium Member
join:2002-07-09
Lanett, AL

JoelC707 to walta

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to walta
said by walta:

I don't understand why anyone would need this equipment.

The whole point of 208V power is 120 volts is available with no transformer necessary any one phase to neutral equals 120 volts.

With a l6-30p plug it is only connected to 2 phases and ground it would only be useful if the electrician had failed to pull a neutral wire.

Is this comment in general or in reference to a residential setting?

To be quite honest, no I don't need it in a residential setting. I have no immediate use case I can really put it to use in and can't honestly think of any.

In a commercial setting, this is mostly used for 120V only equipment when your UPS is a 208/240V model. Though admittedly it's need is greatly diminished when you consider that most equipment these days will take anywhere from 100V to 240V without any care in the world (there is of course a range in there where it won't work but that's beside the point here).
JoelC707

1 recommendation

JoelC707 to tschmidt

Premium Member

to tschmidt
said by tschmidt:

That being said I fail to see what value it has in a residential setting since you already have access to either 120 or 240v without the noise and losses associated with using a transformer.

You're right, I really have no use for this in a residential setting. Even when you consider it's "intended" use being hung behind a UPS, I still don't need it because everything I have can take 240V input so even if I did get a 240V UPS, I can just use it's native output. Even if I did need 120V off a 240V circuit, I'd simply make sure it had a neutral and use it like a MWBC and skip the transformer regardless.

SmokChsr
Who let the magic smoke out?
Premium Member
join:2006-03-17
Saint Augustine, FL

SmokChsr to JoelC707

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to JoelC707
Part of the voltage error if it is 160V output may be that an APC ups doesn't put out true 208V. It's been a while since I had to deal with one of their 208 UPS's but I remember it's a very weird output and not sinusoidal. The transformer may be specifically designed for operation with their UPS.

If that's the case you may get a decent price on ebay for the unit.